METHOD FOR THE PRODUCTION OF HIGH-PURITY ISOPHTHALIC OR TEREPHTHALIC ACID

• US 3,626,001 A
• Filed: 05/09/1968
• Issued: 12/07/1971
• Est. Priority Date: 05/09/1968
• Status: Expired due to Term

• Current Assignee: Emmett H. Burk Jr, Willis C. Keith
• Original Assignee: Emmett H. Burk Jr, Willis C. Keith
• Inventors: Keith, Willis C., Burk, Emmett H. Jr.
• Primary Examiner(s): Gotts, Lewis
• Assistant Examiner(s): Weissberg, R. S.
• Application Number:
  US04/728,037
• Time in Patent Office: 1,307 Days
• Field of Search: 260/524
• US Class Current: 562/413
• CPC Class Codes: C07C 51/265 having alkyl side chains which are oxidised to carboxyl groups
• CPC Class Codes: C07C 63/24 1,3 - Benzenedicarboxylic acid
• CPC Class Codes: C07C 63/26 1,4 - Benzenedicarboxylic acid

Abstract

A method for the production of high purity isophthalic or terephthalic acid from a C8 aromatic hydrocarbon feed stock containing a major amount of the desired isomer of xylene corresponding to the desired acid. The method comprises the twostage oxidation of the isomer of xylene while limiting the amount of orthophathalic acid and water present in the oxidation feed. The feed contains the desired xylene isomer in an alkanoic acid solvent and contains a cobalt catalyst. An alkanal is added to the second stage of the oxidation method and the amount of alkanal added is adjusted with respect to the oxygen partial pressure. An oxidation product representing at least 75 percent conversion of xylene to the corresponding acid is obtained.

Claims

2. The method of claim 1 wherein the alkanoic acid is acetic acid and the alkanal is acetaldehyde.

3. The method of claim 2 further including separating the benzene dicarboxylic acid from the second stage oxidation product to produce a mother liquor and recycling the mother liquor to the first oxidation stage, sufficient feedstock being added to the mother liquor to form said feed.

4. The method of claim 3 wherein the feed contains less than 3 weight percent orthophthalic acid.

5. The method of claim 4 wherein the feed contains about 0.5 to 1.5 weight percent water.

6. The method of claim 5 wherein the first oxidation stage temperature is about 230* to 250* F. and the feed is oxidized for a time sufficient to oxidize at least about 75 percent of the xylene to the corresponding toluic acid.

7. The method of claim 6 wherein the time is about 0.5 to 5 hours.

8. The method of claim 7 wherein a small amount of the alkanal corresponding to the alkanoic acid is added to the first oxidation stage, said amount being sufficient to propagate the oxidation.

9. The method of claim 8 wherein the small amount of alkanal is less than about 0.1 mole per kilogram of feed.

10. The method of claim 7 wherein the cobalt catalyst in the first oxidation stage includes about 25 to 40 percent trivalent cobalt.

11. The method of claim 7 wherein each oxidation stage comprises a plurality of reactors having a temperature drop across the reactor of less than about 50* F. and including recirculating liquid effluent in each said reactor at a rate of at least 0.05 to 5 linear feet per second.

12. The method of claim 11 wherein the temperature drop is about 1* to 10* F.

13. The method of claim 7 wherein the partial pressure of oxygen in the first oxidation stage is about 10 to 50 p.s.i.a.

14. The method of claim 1 wherein at least 65 percent of the cobalt catalyst in the second oxidation stage is the trivalent form of cobalt.

15. The method of claim 14 wherein the amount of alkanal in the second oxidation stage is about 0.1 to 0.3 mole per kilogram of first stage oxidation product and the partial pressure of oxygen is about 25 to 150 p.s.i.a.

16. The method of claim 15 wherein the temperature in the second oxidation stage is about 230* to 250* F. and the first stage oxidation product is oxidized for a time sufficient to provide above 90 percent conversion of the xylene in the feed to the corresponding benzene dicarboxylic acid.

17. The method of claim 7 wherein at least 65 percent of the cobalt catalyst in the second oxidation stage is the trivalent form of cobalt.

18. The method of claim 17 wherein the amount of alkanal in the second oxidation stage is about 0.1 to 0.3 mole per kilogram of first stage oxidation product and the partial pressure of oxygen is about 25 to 150 p.s.i.a.

19. The method of claim 18 wherein the temperature in the second oxidation stage is about 230* to 250* F. and the first stage oxidation product is oxidized for a time sufficient to provide above 90 percent conversion of the xylene in the feed to the corresponding benzene dicarboxylic acid.

20. The method of claim 19 wherein less than 500 p.p.m. xylene are present in the second oxidation stage.

21. The method of claim 20 wherein each oxidation stage comprises a plurality of reactors having a temperature drop across the reactor of less than about 50* F. and including recirculating liquid effluent in each said reactor at a rate of at least 0.05 to 5 linear feet per second.

22. A method for the production of a high-purity benzenedicarboxylic acid selected from the group consisting of terephthalic and isophthalic acid from C8 aromatic hydrocarbon feedstock containing a major amount of the desired isomer of xylene corresponding to desired acid and minor amounts of ortho xylene as an impurity comprising:

first, oxidizing a feed comprising an acetic acid solvent containing about 5 to 15 weight percent of the desired xylene isomer to the corresponding toluic acid in a first oxidation stage with a molecular oxygen-containing gas, said feed containing about 0.05 to 0.15 moles cobalt per kilogram of feed as catalyst, about 0.1 to 4 weight percent water and less than 3 weight percent orthophthalic acid, the first oxidation stage being maintained at a temperature of about 210* to 300* F., a pressure of about 50 to 1,000 p.s.i.a. and an oxygen partial pressure of about 5 to 500 p.s.i.a., the feed being oxidized in the first oxidization stage for a period sufficient to provide a first stage oxidation product wherein at least about 50 percent of the xylene in the feed has been oxidized to the corresponding toluic acid, the cobalt catalyst within the first stage comprising about 10 to 50 percent trivalent cobalt and the remainder bivalent cobalt, the said first stage oxidation product containing less than about 3 weight percent orthophthalic acid and less than about 5 weight percent water, and second, oxidizing the said first stage oxidation product with a molecular oxygen containing gas in a second stage in the presence of about 0.05 to 0.15 mole per kilogram first stage product of cobalt at least about 30 percent of which is in trivalent form, and about 0.05 to 0.5 moles of acetaldehyde per mole of toluic acid in the first stage product at a temperature of about 190* to 275* F., a pressure of about 50 to 1,000 p.s.i.a. and an oxygen partial pressure of about 10 to 500 p.s.i.a. for a period of time sufficient to obtain a second stage oxidation product represenTing at least 75 percent conversion of the xylene in the feed to the corresponding benzene dicarboxylic acid, third, separating the desired terephthalic acid or isophthalic acid to produce a mother liquor and, fourth, recycling the mother liquor to the first oxidation stage while, fifth, removing sufficient orthophthalic acid from the mother liquor so as to maintain the orthophthalic acid content in the first stage oxidation product below about 5 weight percent.

23. A two-stage method for the production of a high-purity benzenedicarboxylic acid selected from the group consisting of terephthalic and isophthalic acid from C8 aromatic hydrocarbon feedstock containing a major amount of the desired isomer of xylene corresponding to desired acid and minor amounts of ortho xylene as an impurity comprising:

first, oxidizing a feed comprising an acetic acid solvent containing about 5 to 15 weight percent of the desired xylene isomer to the corresponding toluic acid in a first oxidation stage with a molecular oxygen-containing gas, said feed containing at least about 0.05 moles cobalt per kilogram of feed as catalyst, about 0.1 to 4 weight percent water and less than 3 weight percent orthophthalic acid, the first oxidation stage being maintained at a temperature of about 210* to 300* F., a pressure of about 50 to 1,000 p.s.i.a. and an oxygen partial pressure of about 5 to 500 p.s.i.a., the feed being oxidized in the first oxidation stage for a period sufficient to provide a first stage oxidation product wherein at least about 50 percent of the xylene in the feed has been oxidized to the corresponding toluic acid, the cobalt catalyst within the first stage comprising about 10 to 50 percent trivalent cobalt and the remainder bivalent cobalt, the said first stage oxidation product containing less than about 3 weight percent orthophthalic acid and less than about 5 weight percent water, and second, oxidizing the said first stage oxidation product with a molecular oxygen containing gas in at least two separate homogeneous reactors in a second stage in the presence of about 0.05 mole per kilogram first stage product of cobalt at least about 30 percent of which is in trivalent form, and about 0.05 to 0.5 moles of acetaldehyde per mole of toluic acid in the first stage product at a temperature of about 190* to 275* F., a pressure of about 50 to 1,000 p.s.i.a. and an oxygen partial pressure of about 10 to 500 p.s.i.a. for a period of time sufficient to obtain a second stage oxidation product representing at least 75 percent conversion of the xylene in the feed to the corresponding benzene dicarboxylic acid, third, separating the desired terephthalic acid or isophthalic acid to produce a mother liquor, fourth, recycling the mother liquor to the first oxidation stage while, fifth, removing sufficient water to maintain the water content in the feed to the first stage between about 0.1 to 4 weight percent.